[Bathing regimen and cold-like upper respiratory tract infections: A case-control study in young children and their...

Objectives　In this study, we investigated associations between a bathing regimen for young children and the incidence of cold-like upper respiratory tract (URT) infections by analyzing URT infection data in young children aged 3-5 years and their parents. We hypothesized that a standardized bathing regimen, defined by water temperature of 39°C-40°C, immersion level from chest to shoulders, and immersion time of 7-20 min, would be effective in preventing viral URT infections, based on evidence from clinical studies of adult bathing. Associations between this regimen and URT infections in young children and parents were examined as the primary and secondary endpoints, respectively.

Young children and parents who consulted or did not consult a medical institution for URT infection between November 1 and 30, 2024, were included. Cases were defined as individuals diagnosed with viral URT infection, and controls were defined as those without URT symptoms who did not undergo medical examination. The study population comprised young children and their caregivers meeting these criteria, totaling 1,968 participants. Bathing elements, including water temperature, immersion level, and bathing duration, as well as the defined bathing regimen, were considered exposures, while URT infection status was the outcome. Associations were evaluated using logistic regression analyses, with odds ratios and 95% confidence intervals (CI) calculated. Lifestyle factors were included as adjustment variables.

In analyses of bathing temperature among young children, multivariate models adjusted for lifestyle factors showed odds ratios of 0.641 (95% CI: 0.442-0.931) for 39°C-40°C and 0.928 (95% CI: 0.627-1.370) for ≥41°C, using ≤38°C as the reference. Multivariate analysis of the bathing regimen in young children yielded an odds ratio of 0.802 (95% CI: 0.644-1.000). A corresponding analysis in caregivers demonstrated an odds ratio of 0.810 (95% CI: 0.692-0.949) after adjustment for lifestyle factors and basic attributes.

Bathing at a temperature of 39°C-40°C was associated with a lower incidence of cold-like URT infections in young children, supporting the study hypothesis. Furthermore, the bathing regimen was associated with reduced infection incidence among caregivers. These findings suggest that structured household bathing practices may contribute to infection control.